Biomedical subjects

Annette Haworth

Publications and source records attributed to Annette Haworth.

5 recordsLinked to original sources

PubMed2005

Impact of selection of post-implant technique on dosimetry parameters for permanent prostate implants.

PURPOSE: To investigate the variability of prostate implant quality indices between three different methods of calculating the post-implant dose distribution. METHODS AND MATERIALS: In a study of 9 permanent prostate implant patients, post-implant dosimetry was carried out using three methods of identifying seed positions within the prostate volume: (1) prostate volumes defined by transrectal ultrasound (TRUS) immediately following implant were registered with shift-film defined seed positions, (2) seeds were identified directly from the post-implant TRUS images, and (3) CT was used to define seed positions and prostate volumes from images acquired at 41-65 days post-implant. For each method, the volume of prostate receiving 90%, 100%, and 150% of the prescribed dose (V90, V100, V150) and the dose delivered to 90% of the prostate volume (D90) were calculated. RESULTS: Post-implant TRUS volumes were within 15% of the preimplant TRUS volumes in 8 of the 9 patients investigated. The post-implant CT volume was within 15% of the preimplant (TRUS) volume in only 3 of the 9 cases. The value of the dosimetry parameters was dependent on the method used and varied by 5-25% for V90, 5-30% for V100, 42-134% for V150, and 9-60% for D90. No simple relationship was found between change in volume and the resultant change in dosimetry parameter. Differences in dosimetry parameters due to source localization uncertainties was found to be small (< or = 10% for V100) when comparing methods (1) and (2). CONCLUSIONS: There are many uncertainties in the calculation of parameters that are commonly used to describe the quality of a permanent prostate implant. Differences in the parameters calculated were most likely a result of a combination of factors including uncertainties in delineating the prostate with different imaging modalities, differences in source identification techniques, and intraobserver variability.

Brachytherapy↗

PubMed2004

Prostate implant evaluation using tumour control probability--the effect of input parameters.

In this paper, we examine the effect of treatment parameters in a model used to evaluate permanent prostate implants. The model considers the prostate to be composed of 12 sub-sections, each sub-section is assigned a cell density based on the probability of finding cancer foci in that sub-section. Wasted dose as a result of the dose rate from the implant falling below a level adequate to counteract repopulation was found to vary by 2-16% over the range of radiosensitivity and repopulation rates considered. Within the model, applied to five dose distributions, the uncertainty in the tumour control probability (TCP) values calculated for each sub-section as a result of differences in the model parameters, was found to be less than 12% in most cases for the good quality implants. The difference in TCP values was much larger for the poor quality implant. Substituting a heterogeneous distribution of alpha for a single mean value resulted in generally lower TCP values though introducing a cutoff value with a Gaussian distribution had a profound effect on the calculated values. Despite uncertainties in the parameters, the model was able to identify sub-sections at risk of local recurrence but as a result of these uncertainties, the TCP values can only be considered in the relative rather than absolute sense.

Brachytherapy↗

PubMed2004

Assessment of i-125 prostate implants by tumor bioeffect.

PURPOSE: A method of prostate implant dose distribution assessment using a bioeffect model that incorporates a distribution of tumor cell densities is demonstrated. This method provides both a quantitative method of describing implant quality and spatial information related to the location of underdosed regions of the prostate. This model, unlike any other, takes into account the likelihood of finding cancer cells in the underdosed region. METHODS AND MATERIAL: The prostate volumes of 5 patients were divided into multiple subsections and a unique cell density was assigned to each subsection. The assigned cell density was a function of probability of finding tumor foci in that subsection. The tumor control probability (TCP) for each subsection was then calculated to identify the location of any significantly underdosed part of the prostate. In addition, a single TCP value for the entire prostate was calculated to score the overall quality of the implant. RESULTS: Adequately dosed subsections scored TCP values greater than 0.80. The TCP for underdosed regions fell dramatically particularly in subsections at higher risk of containing tumor cells. CONCLUSIONS: Despite uncertainties in radiobiological parameters used to calculate the TCP and the distribution of cancer foci through the prostate, the bioeffect model was found to be useful in identifying regions of underdosed prostate that may be at risk of local recurrence due to inadequate dose. Unlike the isodose distribution, the model has the potential to demonstrate that small volumes of tissue underdosed in regions most likely to contain higher numbers of tumor cells may be more significant than larger volumes irradiated to a lower dose but with a lower probability of containing cancer cells.

Brachytherapy↗

PubMed2004

Iodine-125 brachytherapy for prostate cancer: first published Australian experience.

With the emergence of new imaging and implant techniques, prostate brachytherapy has become increasingly popular over the last decade. Brachytherapy promises to deliver twice the biologically effective dose as conventional external beam treatments without increasing the dose to tissues surrounding the prostate. However, there are few or no published Australian series of its efficacy in the clinic. We present the experience of one of the first centres in Australia to offer this service to its patients: a series from Sir Charles Gairdner Hospital in Western Australia. We present data on the efficacy of brachytherapy in maintaining prostate specific antigen levels, as well as the rate of urinary, rectal and sexual complications. Our results compare favourably with other brachytherapy and external beam treatment series. We believe that with the increasing trend towards dose escalation and novel therapies, standardized measurements of success and failure need to be better defined, and that randomized trials comparing modalities are needed to improve the management of prostate cancer.

Aged↗

PubMed2004

Prospective trial of intraoperative radiation treatment for breast cancer.

BACKGROUND: A new device, Intrabeam, is available for intraoperative radiotherapy. We have prospectively examined its feasibility and tolerability in delivering adjuvant breast cancer treatment. METHODS: Thirty-five patients undergoing breast-conserving surgery received targeted tumour bed irradiation consisting of 5 Gy (at 10 mm) in a single fraction. This single intraoperative treatment was used to replace the external beam radiotherapy "boost" that would usually be given in 10 daily treatments following 5 weeks of whole breast irradiation. Patients later completed external beam radiotherapy as usual. Potential toxicities were prospectively assessed fortnightly prior to external beam radiotherapy, weekly during it, and 3 monthly subsequently. RESULTS: The intraoperative radiotherapy was able to be delivered without difficulty, either at time of initial cancer surgery or as a second procedure. When performed as a separate procedure the median operating time was 56 min. The treatment was well tolerated, with only one patient experiencing any grade 3 or 4 toxicities--this was acute grade three itch. There was an overall early breast infection rate of 17%. No unexpected toxicities were seen. CONCLUSIONS: This simple and well-tolerated treatment delivers a useful radiation dose to the area of highest risk of tumour recurrence. The early infection rate is similar to that reported in the literature, for treatments without intraoperative radiotherapy. Whether such a treatment may adequately replace the entire adjuvant radiation therapy treatment for low-risk patients is now being studied in a randomized trial.

Adult↗